Hey-ho, the other day I was wondering what the phonology of Received Pronunciation would be like in about two hundred years (though obviously it wouldn't be called that then) and what it would look like? I doubt we could go another couple of hundred years without needing some sort of spelling reform, especially if the phonology continues to change at the current rate! Here's my suggestion for the sentence "The beige hues on the waters of the loch impressed all, including the French queen, before she heard that symphony again, just as young Arthur wanted", written using Latin letters and the current RP pronunciation. (I would use IPA but I can't be bothered with setting up a keyboard right now): "De baydz yooz on de vautaz o de lok imprest aw, inkloodin de Fwents kveen, bifaw see 'eeud dat sifnee aghen, dzuz az yun Ahta vontit." What say you?

I say wait until you have the keyboard set up. I've got no real idea what values those respellings are supposed to represent (particularly something like eeu; could be anything from some crazy diphthong to a high central unrounded vowel).

1. I'm not seeing any good reason to lose /ʤ/, /ʧ/, or /w/. The last of these has been present in Germanic for as long as it's been a distinct branch of Indo-European. Post-alveolar affricates were present phonetically at least a century ago. If anything, the tendency I'm seeing in contemporary English is towards more affrication/palatalisation, not less. (For instance, affricatisation of final /t/ is common in some urban UK dialects [e.g. Liverpudlian] and seems to be spreading.)2. Similarly, /ð/ and /θ/ have been with us since the earliest times. The tendency among younger speakers in the UK today is not stopping but labialisation, i.e. replacing them with /v/ and /f/ respectively. I find that a much more plausible development.3. What kind of speech has /ɒ/ for of in unstressed position? That screams "spelling pronunciation" to me.4. You really think there will be a phonemic split between /ɪ/ and /ɨ/? Under what conditions exactly?

Some American dialects to seem to tend toward stopping the interdental fricatives, but it's by no means universal. The most significant change observed in American English phonology in recent decades is the Northern Cities Vowel Shift.

You may want to consider the phonological shifts in the Queen's speech over the past 60 years as a starting point for the trends in British English.

I think you may have misunderstood my comment about affrication in Scouse. Here's a brief account of the phenomenon. I'm not sure that anything similar is happening in Estuary, which is where I would look first for emerging trends likely to became mainstream in the coming century.

Also, keep in mind that some changes will be lexeme- or morpheme-specific. That is, they will affect some words or endings but not all. Look, for instance, at the fate of will as an auxiliary and see how that differs from what's happened with the noun will. For instance, it's quite common in casual speech for /ð/ to be dropped in words like the and that, but that doesn't mean there's a more general /ð/-dropping rule taking shape.

I think that the current orthographies of English i.e. Standard American & Canadian/British/Australian must remain largely unchanged because there are so many varieties of spoken English. Even though learners of English as a second language have trouble with the "rules" of English spelling as they are currently, they would have more trouble if they were caught in the middle of a massive spelling rules change. They would have learned one form of spelling only to be told to discard what they had just learned. On the basis of whose pronunciation would the rules be changed? Could there be any international agreement?